Comtech EF Data CDM-500 - Manual (Page 68)

CDM-500 Closed Network Satellite Modem Remote Control
Rev. 1.3 B–3
target. The exception to this is when the controller broadcasts a message (such
as Set time/date) using Address 0, when the target is set to EIA-485 mode.
B.5 Packet Structure
Controller-to-target:
Start of
Packet Target
Address Address
De-limiter Instruction
Code Code
Qualifier Optional
Arguments End of Packet
<
ASCII code60
(1 character)
(4 characters)
/
ASCII code 47
(1 character)
(3 characters)
= or ?
ASCII code
61 or 63
(1 character)
(n characters)
Carriage
Return
ASCII code 13
(1 character)
Example: <0135/TFQ=70.2345{CR}
Target-to-controller:
Start of
Packet Target
Address Address
De-limiter Instruction
Code Code
Qualifier Optional
Arguments End of Packet
<
ASCII code62
(1 character)
(4 characters)
/
ASCII code 47
(1 character)
(3 characters)
= or ?
ASCII code
61, 33 or 42
(1 character)
(From 0 to n
characters)
CarriageReturn
Line Feed
ASCII code
13,10
(2 characters)
Example: >0654/RSW=32{CR}{LF}
Each of the components of the packet is now explained.
B.5.1 Start Of Packet
Controller to Target: This is the character ‘<’ (ASCII code 61)
Target to Controller: This is the character ‘>’ (ASCII code 62)
Because this is used to provide a reliable indication of the start of packet, these two
characters may not appear anywhere else within the body of the message.
B.5.2 Address
Up to 9,999 devices can be uniquely addressed. In EIA-232 applications this value is set
to 0. In EIA-485 applications, the permissible range of values is 1 to 9999. It is
programmed into a target unit using the front panel keypad. Important note: The
controller sends a packet with the address of a target – the destination of the packet.
When the target responds, the address used is the same address, to indicate to the
controller the source of the packet. The controller does not have its own address.